The present invention relates generally to packet switched message handling systems and, more particularly, to a device for quickly classifying previously characterized message headers.
There is increasing interest in providing communications between disparate computer systems and even between networks of differing characteristics. Further, with the availability of very high bandwidth trunk lines, e.g., using fiber optic cables, there is increasing interest in combining traffic from a great variety of sources for transmission through a single trunk line. For wide area networks, packet switching technology is widely used where information to be transmitted is broken into packets of data which are proceeded by headers containing information useful in routing. The header may also identify the source and the destination. Whether truly packet switched or not, most digital communication systems employ message formats in which there is an identifying header of some sort.
For large and complex networks, one standard which is being adopted is that of an asynchronous transfer mode (ATM) switch which operates to transfer data cells of standard characteristics between links in a network. Within an ATM network, routing is typically provided by setting up a path between a source and destination and then including, in the headers for the standardized cells or packets, data which identifies that path to the various switches along the route. However, at various points, a relatively standardized ATM network must interface with disparate systems and convert the message formats of the disparate systems into the standard ATM cell format. A typical situation where this type of interfacing is necessary is at a so-called bridge where a ATM network interfaces with a local area network, e.g., an ethernet or a token ring network. The job of the bridge is essentially to examine all of the traffic on the local area network and, if the destination of a given packet is across the ATM network, i.e., outside the respective local area network, the bridge transfers that message into the ATM network. This process is often referred to as forwarding.
Heretofore, the analysis of message headers to determine appropriate action has been provided by writing a conventional computer program to run on a high speed, but essentially conventional, general purpose processor. The program operates to dissect and test the components of the message header and thereby determine its content. If such a generalized analysis process is performed on every arriving packet or message the time required for such processing rises rapidly as the number of possible header types increases and for high bandwidth systems it may be essentially impossible to conduct such processing. Further, the time required to analyze a message header using this approach, can be highly variable and unpredictable. It is therefor questionable whether this approach can be sufficiently refined to meet the demands of connecting high speed ATM networks to highly varied traffic sources.
Among the several objects of the present invention may be noted the provision of a novel device for classifying message headers of the type which comprises a sequence of bit groups presented successively; the provision of such a device which will direct selected messages to a selected one of a plurality of output paths in accordance with the contents of the message header; the provision of such a device which will classify a message header in a time essentially proportional to the length of that header; the provision of such a device which operates at high speed; the provision of such a device in which the time required to classify a header is predictable; the provision of such a device whose operation can be easily altered to accommodate new types of message headers; the provision of such a device which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.